The forests of the midwestern United States at Euro-American settlement: Spatial and physical structure based on contemporaneous survey data

Abstract

We present gridded 8 km-resolution data products of the estimated stem density, basal area, and biomass of tree taxa at Euro-American settlement of the midwestern United States during the middle to late 19th century for the states of Minnesota, Wisconsin, Michigan, Illinois, and Indiana. The data come from settlement-era Public Land Survey (PLS) data (ca. 0.8-km resolution) of trees recorded by land surveyors. The surveyor notes have been transcribed, cleaned, and processed to estimate stem density, basal area, and biomass at individual points. The point-level data are aggregated within 8 km grid cells and smoothed using a generalized additive statistical model that accounts for zero-inflated continuous data and provides approximate Bayesian uncertainty estimates. The statistical modeling smooths out sharp spatial features (likely arising from statistical noise) within areas smaller than about 200 km2. Based on this modeling, presettlement Midwestern landscapes supported multiple dominant species, vegetation types, forest types, and ecological formations. The prairies, oak savannas, and forests each had distinctive structures and spatial distributions across the domain. Forest structure varied from savanna (averaging 27 Mg/ha biomass) to northern hardwood (104 Mg/ha) and mesic southern forests (211 Mg/ha). The presettlement forests were neither unbroken and massively-statured nor dominated by young forests constantly structured by broad-scale disturbances such as fire, drought, insect outbreaks, or hurricanes. Most forests were structurally between modern second growth and old growth. We expect the data product to be useful as a baseline for investigating how forest ecosystems have changed in response to the last several centuries of climate change and intensive Euro-American land use and as a calibration dataset for paleoecological proxy-based reconstructions of forest composition and structure for earlier time periods. The data products (including raw and smoothed estimates at the 8-km scale) are available at the LTER Network Data Portal as version 1.0.

8000-year doubling of Midwestern forest biomass driven by population- and biome-scale processes

“…We calibrated the relationship between AGWB during the 19th century across the region [Fig. 1A ( 21 )] and contemporaneous fossil pollen samples. We used historical forest survey data from the 19th century to calibrate ReFAB because these data were collected before the massive changes in vegetation structure and composition caused by regional deforestation and land clearance in the late 19th and early 20th centuries ( 22 ).…”

“…( A ) Spatially smoothed AGWB densities at representative Holocene time points. ( B ) Total AGWB pools across the study area with 95% uncertainty estimate: in the PIH (gray); immediately preceding forest clearance (maroon) ( 21 ); and currently (red) ( 35 ). ( C ) Century-to-century changes in total AGWB pools in regional clusters (see Fig.…”

“…4). The final time step is the difference between AGWB immediately preceding forest clearance ( 21 ) and currently ( 35 ).…”

“…2C). Second, the distribution of woody biomass immediately preceding the start of the industrial era ( 21 , 22 ) is often used as a steady-state baseline for carbon cycle modelers. Our analysis shows that the late Holocene terrestrial carbon cycle in eastern North America was not in steady state.…”

“…(C) Century-to-century changes in total AGWB pools in regional clusters (see Fig.4). The final time step is the difference between AGWB immediately preceding forest clearance(21) and currently(35).…”